This invention relates to clamping frames used in vacuum forming machines, and more particularly, to adjustable clamping frames for accommodating varying sizes of plastic sheets to be molded in a vacuum forming machine.
Vacuum forming machines are used in manufacturing plastic signs and the like by draping a heated plastic sheet over a die. The die is perforated, and a vacuum is applied in the interior of the die for conforming by suction the heated plastic sheet to the exact contours of the die. Generally, a clamping frame is used in a vacuum forming machine for securing the plastic sheet to be molded, advancing the plastic sheet to a heat source for plasticizing of the plastic sheet, and then draping or pulling the plastic sheet over the die.
Clamping frames for accommodating various sizes of plastic sheets are not new in the art, and are disclosed, for example, in U.S. Pat. No. 3,133,314, issued May 19, 1964, to Arnould et al., in U.S. Pat. No. 3,841,819, issued Oct. 15, 1974, to Diamond, in U.S. Pat. No. 3,599,959, issued Aug. 17, 1971, to Asenbauer, and in U.S. Pat. No. 4,018,551, issued Apr. 19, 1977, to Shuman.
Also known in the prior art is an adjustable frame structure that has two longitudinal frame members disposed in spaced parallel relation to one another and two transverse frame members disposed in spaced parallel relation to one another. Each of the frame members has clamps secured to it for clamping sheets of plastic to be molded. Each of the two longitudinal frame members has multiple openings extending therethrough longitudinally along the length of the longitudinal frame members, the openings conforming to the cross-sectional shape of the transverse frame members for receiving, retaining, and supporting the transverse frame members.
Because the transverse frame members extend through and rest in the openings of the longitudinal frame members, the longitudinal frame members are free to slide down the transverse length of the transverse frame members, provided any clamps are removed that might inhibit the sliding of the transverse frame member through a longitudinal frame member. The sliding of the longitudinal frame members along the transverse frame members varies the distance between longitudinal frame members and allows the adjustable frame structure to accommodate a variety of sizes of plastic sheets to be molded. Furthermore, because of the multiple openings extending longitudinally along the length of the longitudinal frame members, the transverse frame members can be inserted into openings at varying distances between the two transverse frame members, thereby allowing the adjustable frame structure to accommodate an even greater variety of sizes of plastic sheets to be molded. Of course, to vary the distance between the transverse frame members, the longitudinal frame members must be separated by a distance greater than the transverse length of the transverse frame members in order to remove the ends of a transverse frame member from its current openings.